The morning swoop at the St David’s 2 shopping centre in Cardiff saw officers from South Wales Police use specially trained sniffer dogs to carry out the search as the 500-strong workforce began arriving for work.
Bovis admitted that a number of workers failed to turn up for work - raising suspicions that they had been tipped off by colleagues beforehand.
Bovis Lend Lease project manager Nick Wylie said: “I can’t confirm how many people were off that day.
“The fact that people did not show up could have been a mix of regular absenteeism and workers being warned but we have no evidence of that.”
Bovis called in the police last month after deciding it wanted to carry out a screening on the job, which is one of the -biggest on the firm’s books at the moment.
The results revealed that a dozen employees had either used drugs or been in close contact with drug users in the days leading up to the test.
The 12 were taken aside after the dogs, which are trained to search for cannabis and crack cocaine, circled them and sat at their feet to indicate a suspicion during the raid.
No drugs were found and none of the workers have been prosecuted.
Mr Wylie said the company will take no further action against them.
He said it was all about “sending a signal” to workers that drug abuse was unacceptable and added: “Drugs are an issue not just in Cardiff and not just on this job but nationally.
“It probably sounds trite but at the forefront of our thinking is always the health and safety of both our workers on the site and then the public.”
The raid is the latest in a series of high-profile moves by contractors to clamp down on drug use by staff.
Earlier this year, Laing O’Rourke announced that all staff and subcontractors wanting to work for the firm would have to take drug and alcohol tests.
Mr Wylie promised more raids in the future and added: “We want people to know that if they are working on a -Bovis job, drug abuse will not be tolerated.”
The St David’s 2 project, which started onsite in mid-2006, is due to be completed by early 2010.